The crest factor or peak-to-average ratio (PAR) is a measurement of a waveform, calculated from the peak amplitude of the waveform divided by the RMS value of the waveform. In many wireless communication technologies, the communication signals often have a high peak-to-average ratio (PAR) that can impair the efficiency of the power amplifiers (PAs) employed in wireless base stations. A number of techniques have been proposed or suggested for reducing the PAR in order to improve the efficiency of the power amplifier to thereby allow a higher average power to he transmitted before saturation occurs.
Crest Factor Reduction (CFR) is a digital technique used to reduce the PAR of the transmitted wireless signals. In a wireless transmitter, for example, the CFR is often incorporated with digital pre-distortion (DPD). The DPD serves to linearize the power amplifier to improve the efficiency of the power amplifier. CFR is often used in conjunction with DPD to maximize the transmit average power for a given power amplifier saturation voltage. Frequently, the CFR is positioned after a digital up conversion (DUC) stage and before DPD and/or equalization.
Generally, Crest Factor Reduction techniques employ peak detection and then peak cancellation by subtracting a cancellation pulse from the detected peaks, to reduce the peak amplitude and thereby reduce the PAR. The cancellation pulse is carefully designed to match the signal/channel spectral response. In this manner, peak cancellation only introduces noise inside the signal channel(s), Existing Crest Factor Reduction techniques process the signal sample-by-sample. In sample-based Crest Factor Reduction software implementations, the overhead introduced with processing each sample in software impairs efficiency (e.g., overhead associated with the function call). Thus, a need exists for block-based Crest Factor Reduction techniques, where each block is comprised of a plurality of samples.